html {
  box-sizing: border-box;
  font-size: 62.5%;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
}
*:before, *:after {
  box-sizing: inherit;
}

body {
  width: 100%;
  height: 100vh;
  background-color: #0a0a0a;
  font-family: sans-serif;
}

.wrapper {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  overflow: hidden;
}
.wrapper .block {
  width: calc(100% / var(--amount));
  height: 10px;
  border: 1px solid #307a96;
  animation: oscillate 2s infinite ease-in-out;
}

@keyframes oscillate {
  25% {
    border-color: cyan;
    height: 100px;
  }
  50% {
    border-color: #307a96;
    height: 10px;
  }
}